In a recent paper published in the Annals of Internal Medicine, Bazzano et al. (2014) compared two groups of subjects consuming either a low carb diet (<30%) a low fat diet (<30%). The results of the study have raised eyebrows and have further strengthen the belief that dietary fat consumption does not increase the risk for cardiovascular disease, and may actually reduce it. Let’s jump ahead to the conclusions before breaking down some of the results:
In summary, this 12-month randomized, parallel-group trial showed that a low-carbohydrate diet resulted in greater weight loss and reduction in cardiovascular risk factors than a low-fat diet among obese black and white adults. Restricting carbohydrate may be an option for persons who are seeking to lose weight and reduce cardiovascular risk factors and should be studied further.
Overall the study looks solid. They actually have a larger portion of blacks than in previous studies; most minorities are underrepresented in studies like these. They also controlled for activity levels and caloric intake was similar; some blogs have reported that the low carb group was lower which is incorrect. An interesting thing to note is that these were not extreme dietary comparisons. The low fat group would be better classified as moderate/recommended fat (just under 30%) intake, with only moderate carb intake (about 50%). The low carb was low (<30%), but actually higher than many extreme low carb studies (under 20%); see Table 2 below. ON the surface this seems like a problem, but in many ways its a strength.
First, the low fat diet would be representative of one most would recommend for good health. However, by dropping carb intake and increasing fat to above 40% several (protein also increased to about 25%) cardiovascular disease markers went down significantly, as did weight. How much? Among WHITE participants:
- Low carb lost about 8-10 lbs more
- Low carb also showed a 2% low of FAT mass vs no change for low fat
- Lean mass (muscle and bone mainly) actually increased in the Low carb group
- HDL (good) cholesterol increased only in the Low carb group
- Overall CVD risk decreased
Among BLACK participants:
- Weight loss for Low carb was similar, but not % body fat; likely related to the fact that lean mass increased less than whites. The trend is there.
- HDL cholesterol failed to improve, however triglycerides did decrease.
- Overall CVD risk when down, as did inflammatory markers.
So, going back to the authors conclusions, it would appear that overall, the low carb diet improved weight loss and markers of health more than Low fat. Combined, these results are impressive, but the racial divide raises questions about how to optimize nutrition and weight loss outcomes in blacks, and I would bet latinos. Moreover, the weight loss here without caloric restriction was modest (10-15 lbs) over a year, which is sustainable but likely unacceptable to people looking to lose large amounts of weight. Nonetheless, as more research is published, I think it’s clear that reducing carbohydrate intake should be a first option in weight loss in addition to increase activity. On that final note, this study did not consider activity and exercise, but the data a clear there. If you want to lose weight and you are not exercising/active 5 or more hours each week. Burning 3000 kcal/week plus a reduction of just 300 kcal’s/day can lead to significant weight loss over time.